Patent GB-1235879-A (GB)
Title: Lattice aperture antenna
Inventor: MCMILLAN EDWARD BELLAMY
IPC: H01Q25/00
Filed: 1968-08-19
Abstract: 1,235,879. Aerials. E. B. McMILLAN, 19 Aug., 1968, No. 39610/68. Heading H4A. In an aerial, a lattice wall sandwich is located in the path of radiation from an aperture. Said sandwich comprises an inductive lattice layer consisting of a regular pattern of non-conducting magnetic wall areas perforating conducting electric wall areas, and capacitive layers arranged contiguously with each face of the inductive lattice layer. The thickness of said magnetic wall areas is such that in the equivalent circuit representing the sandwich there is an inductive series component throughout the operating frequency hand. In one embodiment, Fig. 1 (A), a three-layer lattice wall sandwich comprises two outer dielectric plates 1<SP>1</SP>, 1<SP>11</SP> which are assembled in contact with a central perforated metal plate 2<SP>11</SP>. The size of the holes 3<SP>1</SP>, 3<SP>11</SP> in the plate 2<SP>11</SP> diminishes progressively from left to right. In a second embodiment (Fig. 1(B), not shown) the outer dielectric plates are tapered in thickness from left to right, and a pair of perforated metal plates are provided which can be slid over each other to vary the net areas of the perforations effective between the dielectric plates. In a third embodiment, a dielectric plate 9, Fig. 1(C), carries a pattern consisting of non-conductive rings 10<SP>1</SP>, 10<SP>11</SP> surrounding conductive areas 11<SP>1</SP>, 11<SP>11</SP>. In a fourth embodiment (Fig. 1(D), not shown) a dielectric plate carries a pattern consisting of separated conductive rings. A fifth embodiment (Fig. 1(E), not. shown) features a central ribbed perforated conducting plate which is sandwiched between dielectric plates comprising fused silica. In a sixth embodiment (Fig. 1(F), not shown) three plates comprising conductive elements are alternated with four tapered dielectric plates. A seventh embodiment comprises a perforated conductive plate-like member 17, Fig. 1(G), through which hot fluid may be passed for de-icing-. Short tubes connect a pair of spaced apart perforated metal sheets, which are joined at their edges, and the fluid flows in the cavity so formed, over the outer surfaces 18<SP>11</SP> of the tubes.. In an eighth embodiment a sandwich 50, Fig. 5(A), as already described is. provided with an array of rectangular slots which are independently fed (Fig. 5(B), not shown) so that they radiate power at a lower frequency than the aperture which is associated with the. sandwich. An application of the embodiment shown in Figs. 5(A), 5(B) asan aerial system fitted in the nose of an aircraft isdescribed (Figs. 6(A), 6(B), not shown). In another embodiment, a scanning aerial comprises a circularly polarized horn feed 41, Fig. 4, which faces a reflector 40. Said reflector comprises. an alumina/nickel aluminide cermet dielectric layer 42 adhering to a perforated. aluminium. sheet 43, forming a half-sandwich behind which moves a second half-sandwich 44 which is backed by an absorber 45. By relative movement of the two half-sandwiches the registration of the holes in their perforated metal sheets can be adjusted, so that waves of desired frequency and polarization are reflected, other waves being transmitted and absorbed. A radiating aperture for use with a sandwich as described, above is constituted by an opening 31<SP>1</SP> to 31<SP>11</SP>, Fig. 3(A), in the right hand narrow wall of a rectangular waveguide 30. The waveguide is closed at one end 32<SP>11</SP> and power is fed in the other end 32<SP>1</SP>. An inner surface plate 33<SP>11</SP> is hinged at 33<SP>111</SP> on the left hand narrow wall of the waveguide so that it can swing towards the right hand narrow wall thereof. The moving end of the plate 33<SP>11</SP> is in sliding contact with an iris 34<SP>1</SP>, a metal plate slotted so as to be open, as shown, between lines 34<SP>11</SP>, 34<SP>111</SP>. Holes 35<SP>1</SP>, 35<SP>11</SP> remove energy entering the space between the iris 34<SP>1</SP> and the waveguide end 32<SP>11</SP>. A lattice wall sandwich covers, the opening 31<SP>1</SP> to 31<SP>11</SP>. The arrangement may be modified by removing the plate 33<SP>11</SP> and iris 34<SP>1</SP> and feeding from the back instead of the end 32<SP>1</SP>, so forming a type of box horn.